Lots of people, including Ghostcrawler, are talking about interrupts lately. So I'll throw in my two cents. Again, I play mostly PvE, so I'm pretty much ignoring the PvP aspects.
Back in Wrath, a lot of us healers complained that healing was too unforgiving and stressful. Sometimes it felt like you'd miss a heal, and the tank would die. I think Blizzard agreed with that perspective, and changed the balance between healing and tank health for Cataclysm.
But in some respects, it seems like that "unforgiving" element of fights has moved to interrupts. A lot of fights seem to follow the pattern: going fine, going fine, missed interrupt, raid wipes. It's very frustrating for the interrupter, and it's very frustrating for the rest of the raid.
And even the cast times seem to be excessively fast. It seems like the standard interruptible boss spell cast time is 1.5 seconds. That's a really short window. I'm actually rather impressed with our interrupters to be able to hit that small window each time, especially with lag and latency and Halfus knockdowns.1
The other thing that annoys me about interrupts is that Curse of Tongues does not seem to work on most bosses. I mean, here we have a spell that's tailor-made to make interrupting easier, and it's completely useless most of the time. It feels "right" that Blizzard would expect us to use Curse of Tongues to help out the interrupters. The perfect time to use a rarely used skill. And yet, no dice.
If I was to fix anything about interrupts, it would be to make Curse of Tongues and similar debuffs usable in Normal modes, at the very least. That would bring the 1.5 second cast time up to ~2 seconds for Normal modes. I think this would make the interrupts more forgiving, and be more balanced for that level of raiding. Heroic bosses can remain immune to Curse of Tongues, upping the challenge for interrupters playing at the higher level.
1. Honestly, WTF is this? Rotating mages ice-blocking and stun-break CDs through the last knockdown so we can interrupt? Did this not strike anyone at Blizzard as slightly excessive?